fix(librarian): register JanitorCleanupFavoritesTask in scribe priority

[ajslater]

Summary

• JanitorCleanupFavoritesTask was missing from _SCRIBE_TASK_PRIORITY, so get_task_priority() raised ValueError: tuple.index(x): x not in tuple whenever the task reached the scribe queue. The task was wired into janitor dispatch, nightly queueing, and the admin task map — only the priority tuple was missed.
• Effect: the Cleanup Orphans Favorites admin task (and the nightly run) stayed stuck on pending forever; the librarian logged a traceback originating in scribed.py:put -> priority.py:70.
• Fix: add JanitorCleanupFavoritesTask to the priority tuple next to the other orphan-cleanup tasks, and reorder Bookmarks/Settings to mirror _NIGHTLY_TASK_CLASSES so the two tuples stay in sync.

Reviewer notes

• No tests currently cover get_task_priority / _SCRIBE_TASK_PRIORITY. Verified manually that get_task_priority(JanitorCleanupFavoritesTask()) returns a valid (int, float) tuple, and that every ScribeTask subclass in _NIGHTLY_TASK_CLASSES is also present in _SCRIBE_TASK_PRIORITY.
• make fix is currently broken on macOS due to bin/fix-docker.sh using mapfile (Bash 4+ only; macOS ships Bash 3.2). Surfaced here as a separate workflow issue — not addressed in this PR.

Test plan

• Trigger Cleanup Orphans Favorites from the admin Tasks panel and confirm it transitions out of pending and completes.
• Trigger Janitor Nightly and confirm the favorites cleanup runs without a traceback.

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